Many buildings, notably industrial or office premises, have ventilation apertures in the walls or roofs thereof through which the flow of air is controlled by dampers, shutters, louvres or the like. For convenience, the term damper will be used herein to denote in general all forms of closure member which act to close an aperture. In the event of a fire, it is necessary that the dampers be closed to minimise the access of air to the affected area. Hitherto, the operation of the dampers has been achieved by thermally responsive elements which automatically close the dampers in response to a temperature rise detected by a suitable sensor or by the use of a bimetallic strip to actuate the closure mechanism. However, this results in dampers which are either fully closed or fully open and which require manual re-setting in the event that they are accidentally actuated. Furthermore, it is not possible to have some dampers open in an affected area where others are closed, which may give rise to inflexibility in operating the damper system.
As an alternative to thermally actuated mechanical closure means, it has been proposed to operate each individual damper by an electro-mechanical means from a central control unit. Such a system comprises a series of damper actuating motors or the like each connected to the central control unit via a cable so that each motor receives its instructions from the control unit and can be operated independently of the others. However, this requires major expense and disruption of the premises during installation of the system due to the number of cables which must be provided. Furthermore, if any one of the cables is damaged at any time, control of the damper which that cable serves is lost.
We have now devised a system for controlling the operation of a system of dampers which reduces the number of cables required, which enables the dampers to be operated individually and which enables control of a damper to be maintained even where a cable is damaged.